End-of-current trim for common rail fuel system

ABSTRACT

Fuel is injected by energizing a solenoid of a fuel injector for an on-time that terminates at a first end-of-current timing. An end-of-current trim is determined at least in part by estimating a duration between an induced current event in a circuit of the solenoid and a valve/armature interaction event. An induced current event occurs when an armature abruptly stops, and a valve/armature interaction event occurs when the armature couples with or de-couples from the valve member. Fuel is injected in a subsequent injection event by adjusting the end-of-current timing by the end-of-current trim.

TECHNICAL FIELD

The present disclosure relates generally to trimming electronic controlsignals for fuel injectors, and more particularly to determining anend-of-current trim for certain electronically controlled fuelinjectors.

BACKGROUND

Electronically controlled fuel injectors typically utilize a solenoid toopen and close a small pressure control valve to facilitate injectionevents. For many years the control valve structure of theseelectronically controlled fuel injectors utilized a solenoid with anarmature attached to move with a valve member. Each injection eventinvolves energizing a solenoid to move the armature/valve member betweentwo stops against the action of a biasing spring. Depending upon whetherthe valve is two way or three way, one or both of the stops can be valveseats. Soon after the adoption of these electronically controlled fuelinjectors, engineers discovered that each fuel injector respondedslightly differently to the same control signal. In addition, theresponse of an individual fuel injector to the same control signal couldvary significantly over the life of the fuel injector. These variancesfrom nominal behavior can be attributed to geometric tolerances, slightdifferences between otherwise identical components, wear, temperatureand other factors known in the art as well as other possibly still yetunknown causes.

Engineers soon began devising ways of estimating or measuring how muchthe behavior of an individual fuel injector deviated from an expectednominal behavior in response to a known control signal, and thenapplying trimmed control signals so that the individual fuel injectorbehaved more like a nominal fuel injector. For instance, if a nominalcontrol signal resulted in the fuel injector injecting slightly too muchfuel, the trimmed control signal might have a slightly briefer durationthan the nominal control signal resulting in the fuel injector injectingabout the same amount of fuel as would be expected in response to thenominal control signal. These slight control signal changes are oftenreferred to in the industry as electronic trims.

U.S. Pat. No. 7,469,679 teaches a strategy for trimming electroniccontrol signals to an electronically controlled valve in which thearmature and valve member are attached together and move as a unit. Inthat specific example, a solenoid is energized to move the armature andvalve member from contact with a first seat (stop) to contact with asecond seat (stop) to open a pressure control passage to either a highpressure source or a low pressure drain to facilitate an injectionevent. The armature and valve are returned to their original positionswhen the solenoid is de-energized under the action of a return spring.When the valve member hits a seat, the motion of the armature abruptlystops, causing a brief induced current event in the electronic circuitassociated with the solenoid. By comparing the timing of the inducedcurrent event to the expected timing of when the valve member shouldcontact the seat, one can measure how much the behavior of thatindividual electronically controlled valve deviates from nominal, andconstruct a trimmed control signal that causes the valve member tocontact the seat at the expected timing, resulting in a fuel injectionevent that more closely resembles a nominal fuel injection event.

More recently, electronically controlled valves for fuel injectors havebecome more sophisticated to the point where, in some instances, thearmature can move with respect to the valve member. For instance, onesuch valve allows the armature to overtravel and decouple from the valvemember after the valve member has contacted its seat. Unfortunately,utilizing the trim determination strategy associated with valves inwhich the armature and valve member move as a unit will not work becausethe induced current event, if any, does not occur responsive to thevalve member contacting its seat. It is valve closure timing, ratherthan armature motion, that is most important to ascertaining fuelinjection variations. While these more sophisticated valves may allowfor performance advantages over their previous counterparts, the causesof valve behavior variations remain. Because the old strategies are nolonger applicable, developing electronic trim for control signals tothese more sophisticated electronically controlled valves can beproblematic.

The present disclosure is directed toward one or more of the problemsset forth above.

SUMMARY

In one aspect, a method of operating a fuel injector includes injectingfuel in a first injection event by energizing a solenoid of the injectorfor a first on-time that terminates at a first end-of-current timing. Anend-of-current trim is determined at least in part by estimating aduration between an induced current event in a circuit of the solenoidand a valve/armature interaction event. Fuel is then injected in asecond injection event, which is subsequent to the first injectionevent, by energizing the solenoid for a second on-time, which isdifferent from the first on-time, and terminates at a secondend-of-current timing that is the first end-of-current timing adjustedby the end-of-current trim.

In another aspect, a common rail fuel system includes a high pressurepump fluidly connected to a common rail. A plurality of fuel injectorsare fluidly connected to the common rail, and each of the fuel injectorsincludes a valve and a solenoid with an armature. An electroniccontroller is in control communication with the high pressure pump andeach of the plurality of fuel injectors, and includes an end-of-currenttrim determination algorithm configured to determine an individualend-of-current trim for each of the plurality of fuel injectors. Theend-of-current trim determination algorithm is configured to determineeach end-of-current trim at least in part by estimating a durationbetween an induced current event in a circuit of the solenoid and avalve/armature interaction event for each of the plurality of fuelinjectors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an engine with a common rail fuel systemaccording to the present disclosure;

FIG. 2 is a side sectioned view of one of the fuel injectors from theengine of FIG. 1;

FIG. 3 is a schematic view of the electronically controlled valve forthe fuel injector of FIG. 2 at the initiation of a fuel injection event;

FIG. 4 is a view of the electronically controlled valve of FIG. 3 afterthe solenoid has been energized and the armature has contacted its upperstop;

FIG. 5 is a schematic view of the electronically controlled valve ofFIGS. 3 and 4 after the solenoid has been de-energized and the valvemember has moved back downward into contact with its seat;

FIG. 6 shows the electronically controlled valve of FIGS. 3-5 when thearmature has overtraveled and contacted an overtravel stop;

FIG. 7 shows the electronically controlled valve of FIGS. 3-6 after thearmature has returned to its original configuration;

FIG. 8 is a graph of current verses time for example fuel injectionevents;

FIG. 9 is a graph of armature position verses time for the fuelinjection events of FIG. 8;

FIG. 10 is a graph of valve position verses time for the fuel injectionevent of FIG. 8;

FIG. 11 is a graph of current verses time for diagnostic eventsaccording to the present disclosure;

FIG. 12 is a graph of armature position verses time for the diagnosticevents of FIG. 11;

FIG. 13 is a graph of valve position verses time for the diagnosticevents of FIG. 11;

FIG. 14 is a graph of second armature bounce delay verses dwell time fora plurality of diagnostic events including those of FIG. 11;

FIG. 15 is a look up table of end-of-current trim verses overtravelreturn delay according to another aspect of the present disclosure; and

FIG. 16 is a logic flow diagram that includes an end-of-current trimdetermination algorithm according to the present disclosure.

DETAILED DESCRIPTION

Referring initially to FIGS. 1 and 2, an engine 10 is equipped with acommon rail fuel system 11 that includes a common rail 15. Engine 10 maybe a compression ignition engine, and common rail 15 may containpressurized distillate diesel fuel. Common rail fuel system 11 includesa high pressure pump 16 fluidly connected to the common rail 15, and aplurality of fuel injectors 12 that are each fluidly connected to commonrail 15 at an inlet 13. High pressure pump 16 draws fuel from a tank 17,which is also fluidly connected to drains 14 of the fuel injectors 12. Apressure sensor 19 may communicate pressure information in common rail15 to an electronic controller 18. Electronic controller 18 is incontrol communication with the high pressure pump 16 and each of theplurality of fuel injectors 12 (only one control communication link isshown). In particular, electronic controller 18 may be in controlcommunication with an electronically controlled valve 22 of each of thefuel injectors 12. The electronically controlled valve 22 includes asolenoid made up of a coil 23 and an armature 24 operably coupled to avalve member 25 to open and close a flat seat 39.

Each fuel injector 12 includes an injector body 20 that defines an inlet13, a drain 14 and a nozzle outlet 30. Fuel is injected by moving aneedle check 31 from a downward closed position, as shown, to an upwardopen position to fluidly connect nozzle outlet 30 to inlet 13. Controlover this process is accomplished by changing pressure in a needlecontrol chamber 33. Needle check 31 includes a closing hydraulic surface32 exposed to fluid pressure in needle control chamber 33. Needlecontrol chamber 33 is fluidly connected to a pressure control passage 34that opens through seat 39. When the valve member 25 is in its downwardposition in contact with seat 39, pressure control passage 34 is closed,and the prevailing pressure in needle control chamber 33 is the pressureassociated with inlet 13 and common rail 15. When the valve member 25moves out of contact with seat 39, needle control chamber 33 becomesfluidly connected to low pressure drain 14 by way of pressure controlpassage 34 to allow pressure in needle control chamber 33 to drop, andallow needle check 31 to lift to its open position to commence aninjection event.

Referring in addition to FIGS. 3-7, electronically controlled valve 22includes an armature 24 that is operatively coupled to valve member 25by a pin 26. A valve spring 27 is operably positioned to bias pin 26 andvalve member 25 downward toward its closed position in contact with seat39. An overtravel spring 28, which has a lower pre-load than valvespring 27, is operably positioned to bias armature 24 into contact witha contact shoulder 38 of pin 26. FIGS. 2 and 3 show an electronicallycontrolled valve 22 with solenoid coil 23 de-energized, with armature 24in contact with pin 26, and valve member 25 in contact with seat 39 toclose pressure control passage 34. FIG. 4 shows the positioning of thecomponents after coil 23 has been energized. When this occurs, armature24 is magnetically pulled in the direction of coil 23 until pin 26contacts upper stop 37. High pressure in pressure control passage 34pushes valve member 25 upward to open the fluid connection betweenneedle control chamber 33 and drain 14, relieving pressure on closinghydraulic surface 32 of needle check 31. When this occurs, needle check31 lifts to commence an injection event. Toward the end of an injectionevent, solenoid coil 23 is de-energized. When this occurs, valve spring27 pushes pin 26, armature 24 and valve member 25 downward until valvemember 25 contacts seat 39 (FIG. 5). Armature 24 continues in itsdownward movement de-coupling from pin 26, further compressingovertravel spring 28, and eventually contacting with and bouncing off ofovertravel stop 29 (FIG. 6). Shortly thereafter, armature 24 moves backupward under the action of spring 28 and remaining momentum afterbouncing off of overtravel stop 29 to eventually contact shoulder 38 ofpin 26. This returns the electronically controlled valve 22 to itsoriginal configuration as shown in FIG. 7.

Thus, unlike older electronically controlled valves known in the art,the electronically controlled valve 22 of the illustrated embodimentincludes an overtravel feature that allows the armature 24 to move withrespect to the valve member 25 after valve member 25 has contacted seat39. There are several reasons outside of the scope of this disclosurefor why an electronically controlled valve 22 having an overtravelfeature can provide performance improvements over the older valves wherethe armature was directly attached to move with the valve member at alltimes. However, one reason is that the de-coupling of the armature 24from the pin 26 when the valve member 25 contacts seat 39, reduces theincidence of bounce off the seat 39 to reduce the likelihood ofsecondary injections, which has sometimes plagued fuel injectors of theprior art.

Referring now in addition to FIGS. 8-10, the current in the solenoidcircuit (FIG. 8) verses time is shown adjacent armature position (FIG.9) and valve position

(FIG. 10) for example injection events according to a nominal trace(solid line, FIGS. 8-10), an uncorrected trace (dashed line, FIGS. 8-10)and a corrected or trimmed trace (dot/dash line, FIGS. 8-10). Theinjection event begins at TO at a beginning-of-current (BOC) to coil 23.When this occurs, as expected the armature 24 and valve member 25 movetoward their upward open position until stopping at T1, whichcorresponds to the configuration shown in FIG. 4. Around the time of T1,or shortly thereafter, the needle check 31 lifts to its open positionand the spray of fuel out of nozzle outlet 30 commences. Atend-of-current (EOC) the solenoid coil 23 is de-energized. The armature24 and valve member 25 then move downward toward their closed positions.At or around time T2, when seat 39 becomes closed as shown in FIG. 5,the injection event ends. At time T3 (FIG. 6), during armature 24overtravel, the armature contacts overtravel stop 29. Of interest is thegraph of FIG. 8 showing induced current events 61N and 61U associatedwith contacting the overtravel stop 29 for the curves associated withthe nominal and uncorrected injection events, respectively. The timebetween the end-of-current (EOC), and the induced current event 61 isidentified as an armature bounce delay (ABD) 66 in the graph of FIG. 8.Those skilled in the art will appreciate that the electronic controller18 can sense the timing of the induced current event 61 in the circuitassociated with solenoid coil 23, and therefore be able to preciselydetermine the duration of the armature bounce delay 66. Of interest isnoting that the difference between T3 (nominal) and T3′ (un-corrected)is different than the time between T2 and T2′. Thus, while theelectronic controller 18 can precisely sense the timing of T3,controller 18 cannot directly sense the valve closing event T2, makingit difficult to arrive at a end-of-current trim 60 that would cause thevalve 22 to close at the desired timing T2. In other words, by adjustingthe nominal control signal of FIG. 8 by the end-of-current trim 60, theelectronically controlled valve 22 can be made to close at about thesame time as T2, resulting in an injection event that more closelyresembles a nominal injection event (solid line, FIG. 8-10). Thoseskilled in the art will appreciate that the end-of-current trim 60 isdifferent from the difference between timing T3 and T3′. The presentdisclosure is directed to determining a correct end-of-current trim 60when the valve closing event T2 cannot be directly sensed, but thearmature bounce event associated with timing T3 can be sensed. Thoseskilled in the art will appreciate that the timing of the end ofinjection (EOI) is associated with the valve closing timing T2, ratherthan the armature bounce event associated with timing T3.

Because of component differences caused by geometrical tolerances,variations in spring loads, differences in friction forces, and manyother factors, the overtravel action of each electronically controlledvalve 22 of each fuel injector 12 will be different. Thus, attempting toarrive at an end-of-current trim only by looking at the differencebetween the nominal armature bounce event at T3 and the uncorrectedarmature bounce event at T3′ can lead to an inaccurate end-of-currenttrim determination. However, the present disclosure insightfullyrecognizes that the time between T3 when the armature hits overtravelstop 29, and time T4 when the armature returns to contact with pin 26,is highly correlated with the time difference between valve closing atT2 and armature bounce at time T3. This insight makes sense because, ifone can characterize the motion of the armature 24 with respect to thevalve member 25 at one portion in the overtravel mode, one canaccurately predict what that motion looks like elsewhere during theovertravel mode.

The logic flow diagram of FIG. 16 along with the graphs of FIGS. 11-15are included to show one example way of leveraging this insight for anelectronically controlled valve 22 in which the armature 24 can movewith respect to the valve member 25. This strategy can be used to arriveat an accurate end-of-current trim 60 to adjust a control signal to anindividual fuel injector 12 to produce an injection event closelyresembling a nominal injection event. Those skilled in the art willappreciate that, not only does the overtravel motion of each individualvalve 22 vary from one another, but that motion also varies during thelife of each individual fuel injector 12. Thus, determining an accurateend-of-current trim 60 for an individual injector 12 may not remainaccurate over the life of the fuel injector. Thus, an individualend-of-current trim 60 may need to be determined a plurality of timesover the life of the injector 12. For instance, one end-of-current trim60 may be determined when the fuel injector 12 is put in service,another updated end-of-current trim 60 may be determined after abreak-in period, and then one or more additional times during the lifeof that individual fuel injector 12 in order to maintain an accurateend-of-current trim 60.

Those skilled in the art will recognize that accurately sensing thetiming of an induced current event has been used in the past to directlydetermine electronic trim for fuel injectors equipped withelectronically controlled valves in which the armature does not movewith respect to the valve member, such as by being affixed thereto. Inthose circumstances, the valve returning to its seat coincides with theinduced current event induced by the armature coming to an abrupt stopwhen the solenoid coil is de-energized. However, when the electronicallycontrolled valve 22 has a structure that permits armature movement withregard to the valve member 25, the induced current event 61 occurs at adifferent timing than valve member 25 contacting seat 39. Neverthelessthe present disclosure proposes a strategy that utilizes the samefeedback mechanism of the armature contact with overtravel stop 29 (FIG.6), but utilizes this information in a new way to characterize theovertravel delay from valve return (T2, FIG. 5) to armature bounce (T3,FIG. 6) so that variances from nominal can be compensated for.

Referring now in addition to FIGS. 11-15, the solution involvesintroducing a first diagnostic on-time 63 in the solenoid coil 23 toproduce enough valve lift to provide a full overtravel response from thevalve 22. As used in this disclosure, full overtravel response meansthat the armature 24 has enough momentum to strike the overtravel stop29 during its overtravel motion. In a preferred version, the diagnosticsof the present disclosure are performed between regular injection eventssuch that the first diagnostic on-time 63 provides a full overtravelresponse from the valve, but not enough to produce any fueling, and maybe an insufficient on-time for the armature 24 to reach its upper stop37 (FIG. 4). The first armature bounce delay 66 is measured from the endof the first diagnostic on-time 63 to the induced current event 61A thatoccurs when the armature 24 contacts overtravel stop 29. A seconddiagnostic on-time 64 is then introduced at no dwell offset or a smalldwell offset from the timing of the induced current event 61A. Anexample of such a waveform is shown by dotted lines in FIG. 11. At thistiming, one could expect the armature momentum to provide assistance tothe valve lift of the second diagnostic on-time 64. Together, the firstdiagnostic on-time 63 separated by dwell 65 from the second diagnosticon-time 64 can be considered a diagnostic event 62 according to thepresent disclosure. Next, electronic controller 18 may adjust theduration of the second diagnostic on-time 64 so that sufficient lift isachieved by the forced applied by the second wave form to again achievefull overtravel response. This may be done by monitoring the secondarmature bounce delay 67, and then increasing the duration of the seconddiagnostic on-time 64 until it approximates that produced by the firstdiagnostic on-time 63. It may be helpful that the armature 24 does notreach upper stop 37 during this process in order to reduce signalprocessing complications. Once the duration of the second diagnosticon-time 64 is set, the dwell 65 between the first and second wave formsis swept.

During the dwell sweep, a plurality of different diagnostic events 62are performed with the dwell 65 being swept from the value correspondingto the first armature bounce delay 66 (dotted line, FIG. 11) through atiming where a trough in the second armature bounce delay 67 is detected(FIG. 14). The second armature bounce delay 67 corresponds to the timebetween the end-of-current of the second diagnostic on-time 64 throughto the induced current event 61B associated with armature bounce off ofovertravel stop 29. In other words, depending upon the dwell 65, thesecond armature bounce delay 67 will change as shown in FIG. 11. Inparticular, FIG. 11 shows an induced current event 61B associated withthe solid line diagnostic on-time 64, a dotted line induced currentevent 61B′ associated with a diagnostic on-time 64′ corresponding to thedotted line, and an induced current event 61B″ corresponding to thediagnostic on-time 64″ shown in FIG. 11 with a dashed line. The presentdisclosure insightfully recognizes that, at a certain dwell D (FIGS. 11,14) the beginning of current for the second diagnostic on-time 64corresponds to when the armature 24 has contacted contact shoulder 38 ofpin 26. At this timing, a minimum amount of valve lift occurs as shownin FIG. 13, because the valve lift associated with the second diagnosticon-time 64 does not get the benefit of armature momentum still existingfrom the motion caused by the first diagnostic on-time 63. FIG. 14 showsa plot of different second armature bounce delay 67 verses dwell 65 withthe local minimum occurring at minimum valve lift at dwell D, which isshown in FIGS. 11-13 by the solid line.

By identifying the dwell D associated with the minimum lift, one caninfer that the start of current for the second diagnostic on-time 64occurred when the armature 24 re-contacted pin 26. This in turn allowsfor the calculation of the overtravel return delay (ORD) 68, which isthe time between the induced current event 61A associated with thearmature contacting overtravel stop 29, and the timing at which thearmature contacts shoulder 38 of pin 26 (Beginning of current ofdiagnostic on time 64 at dwell D). Because the motion of the armature 24before and after the bounce off of overtravel stop 29 are related due toindividual mass properties and the like, the overtravel return delay 68is correlated to an accurate end-of-current trim 60. As used in thisdisclosure, overtravel return delay 68 means the difference between thefirst induced current event (61A)(FIG. 11) associated with time T3 (seeFIG. 9), and the valve/armature interaction event associated with T4(see FIG. 9). As used in this disclosure, an induced current event 61means a current induced in the circuit for the solenoid coil 23 causedby an abrupt change in the motion of armature 24, such as by contactingovertravel stop 29. A valve/armature interaction event according to thepresent disclosure means the occurrence of when the armature 24 eitherstarts moving with respect to, or stops moving with respect to, thevalve member 25. Thus, according to the present disclosure avalve/armature interaction event occurs at time T2 (FIG. 10) when thearmature 24 begins moving with respect to valve member 25 forovertravel, and a second valve/armature interaction event occurs at timeT4 (FIG. 9) when the armature finishes its overtravel and recouples withpin 26 by contacting contact shoulder 38.

Reiterating, the present disclosure recognizes that the time from thearmature 24 hitting the overtravel stop 29 (induced current event 61A,FIG. 11) to the beginning of current of the second diagnostic on-time 64(corresponding to the trough in the graph of FIG. 14 at dwell D) is theovertravel return delay 68 and, is highly correlated to the time betweenthe valve member 25 hitting at seat 39 (T2) and the time that thearmature hits its overtravel stop 29 (T3). Recognizing this correlation,a look up table of overtravel return delay (ORD) verses end-of-currenttrim 60, such as that shown in FIG. 15, can be prepared and stored onelectronic controller 18 before engine 10 is put into service. In otherwords, this correlation likely does not vary significantly over the lifeof the fuel injector and therefore can be prepared beforehand.

Those skilled in the art will appreciate that each diagnostic event 62of each dwell 65 in the sweep of different dwells may be performed aplurality of times in order to average the results for each individualdwell 65 to get more accurate results. When the dwell sweep is performedby gradually increasing dwell 65, the dwell may be incremented in a fineenough increment in order to produce a clear minimum at dwell D in thesecond armature bounce delay 67 as shown in FIG. 14. After determiningthe end-of-current trim 60 using the look up table from FIG. 15, thesubsequent injection event may be performed as shown in FIGS. 8-10 tocause the fuel injector 12 to close valve 22 at a timing associated witha fuel injector exhibiting nominal behavior, to produce a more accurateinjection event, which means closer to nominal.

INDUSTRIAL APPLICABILITY

The present disclosure finds general applicability to electronicallycontrolled valves that permit relative motion between an armature and anassociated valve member. The present disclosure finds specificapplicability to common rail fuel systems that utilize an electronicallycontrolled valve to control injection events in which the electronicallycontrolled valve includes an overtravel feature. Overtravel permits thearmature to overtravel and move with respect to valve member 25 afterthe valve member 25 contacts seat 39 to end an injection event. Otherrelative motion armature and valve structures might also apply theinsights of this disclosure.

Referring now to FIG. 16, electronic controller 18 includes a fuelinjector control algorithm 70 that includes a fueling algorithm 71 andan end-of-current trim determination algorithm 80. The end-of-currenttrim determination algorithm 80 is configured to determine an individualend-of-current trim 60 for each of the plurality of fuel injectors 12.Each end-of-current trim 60 is determined at least in part by estimatinga duration between an induced current event 61 in a circuit of solenoidcoil 23 and a valve/armature interaction event for each of the pluralityof fuel injectors 12.

At oval 72 algorithm 70 starts. At box 73, electronic controller 18determines a nominal injection control signal in a manner well known inthe art. At box 74, the control signal is adjusted with anend-of-current trim 60, if any, before performing an injection event atblock 75. For instance, fuel may be injected in a first injection eventby energizing solenoid coil 23 of a fuel injector 12 for a first on-timethat terminates a first end-of-current timing, which is identified asEOC in FIG. 8. At query 76, electronic controller 18 queries whether todetermine an end-of-current trim 60. For instance, if electroniccontroller 18 has determined that the fuel injectors 12 have achievedbreak in, query 76 may return a yes and proceed to execute theend-of-current trim determination algorithm 80.

At box 81, the first diagnostic on-time 63 and the second diagnosticon-time 64 for the diagnostic events 62 are set. At box 82, the firstarmature bounce delay 66 is measured by detecting the time betweenend-of-current for the first diagnostic on-time 63 and the inducedcurrent event 61A corresponding to armature bounce (FIG. 11). Next, atbox 83 the initial dwell is set to correspond to about the timing (61A)of the first armature bounce delay (ABD1). A diagnostic event 62 is thenperformed at box 84. The second armature bounce delay 67 is measured andstored at box 85 in order to compare the second armature bounce delays67 for other diagnostic events. At box 86, the dwell 65 is incremented.At query 87, the algorithm 80 determines whether the dwell sweep hasbeen completed. If not, the logic loops back to block 84 to performanother diagnostic event 62 with a different dwell 65. The secondarmature bounce delay 67 is then measured and recorded at box 85, andthe dwell is again incremented at box 86. After this loop is performedenough times to gather enough data to construct a graph of the typeshown in FIG. 14, query 87 will return a yes and advance to box 88.Thus, the dwell 65 of each diagnostic event 62 in the sweep is differentfor each of the plurality of diagnostic events. At box 88, the logicidentifies which diagnostic event 62 of the plurality of diagnosticevents has a second armature bounce delay 67 that is smaller than thearmature bounce delay of the remaining diagnostic events of theplurality of diagnostic events, as identified in the graph of FIG. 14.At box 89, the overtravel return delay 68 for the identified diagnosticevent 62 is calculated. Next, at box 90, the end-of-current trim 60 maybe determined based upon the calculated overtravel return delay 68, suchas by utilizing a look up table of the type suggested by FIG. 15. Next,the logic loops back to continue regular fueling according to thefueling algorithm 71.

The end-of-current trim 60 can be considered as being determined atleast in part by estimating a duration (overtravel return delay 68)between an induced current event 61A in the circuit of solenoid coil 23and a valve/armature interaction event (armature 24 contacting contactshoulder 38 at T4). When box 74 is again executed, for a secondinjection event which is subsequent to the earlier first injectionevent, the solenoid coil 23 is again energized for a second on-time(dot/dash in FIG. 8), which is different from the first on-time andterminates at a second end-of-current timing that is the firstend-of-current timing (EOC in FIG. 8) adjusted by the end-of-currenttrim 60.

Preferably, the multiple diagnostic events associated with theend-of-current trim determination algorithm 80 are performed betweeninjection events and done so without causing any fueling. Nevertheless,some fueling could occur during the execution of the end-of-currentdetermination algorithm 80 without departing from the scope of presentdisclosure. In other words, the diagnostic on-times 63 and 64 arepreferably chosen to be sufficiently long to move the valve member 25out of contact with seat 39, but insufficiently long to inject fuel fromfuel injector 12.

Those skilled in the art will appreciate that each injection event forfuel injector 12 includes moving valve member 25 out of contact withseat 39 to open pressure control passage 34 to drain 14, and then movingthe valve member 25 back into contact with seat 39 to close pressurecontrol passage 34. Movement of the valve member 25 includes movingarmature 24, which is operably coupled to valve member 25. In theillustrated structure, armature 24 overtravels after valve member 25contact seat 39 to end an injection event. Preferably the end-of-currenttrim determination algorithm 80 and its associated diagnostic events 62occur after a first regular injection event but before a secondinjection event according to the regular fueling algorithm 71. As bestshown in FIG. 11, the solenoid coil 23 is energized and de-energizedtwice during each diagnostic event 62.

Preliminary data suggests that accurate determination of anend-of-current trim 60 according to the present disclosure can correctup to 3% fueling change per injection event as the overtravel motion ofthe electronically controlled valve 22 changes with wear, break in andage. In addition, the end-of-current trim 60 can help to linearize thedelivery curve and potentially reduce minimum delivery control, andpotentially correct for other aging effects that may change the valveseating time. The technique of the present disclosure could alsopotentially be used as a diagnostic to indicate that there isinsufficient overtravel in a specific armature 24 for one of the fuelinjectors 12, which can suggest an insufficient sealing force of thevalve member 25 on seat 39. Those skilled in the art will appreciatethat insufficient sealing force can be exhibited by excessive fuelingfrom an extended end of injection (EOI) or possibly even merging twoadjacent fueling shots into one.

It should be understood that the above description is intended forillustrative purposes only, and is not intended to limit the scope ofthe present disclosure in any way. Thus, those skilled in the art willappreciate that other aspects of the disclosure can be obtained from astudy of the drawings, the disclosure and the appended claims.

1.-10. (canceled)
 11. A common rail fuel system comprising: a commonrail; a high pressure pump fluidly connected to the common rail; aplurality of fuel injectors fluidly connected to the common rail, andeach of the fuel injectors includes a valve and a solenoid with anarmature; an electronic controller in control communication with thehigh pressure pump and each of the plurality of fuel injectors, andincluding an end-of-current trim determination algorithm configured todetermine an individual end-of-current trim for each of the plurality offuel injectors; wherein the end-of-current trim determination algorithmis configured to determine each end-of-current trim at least in part byestimating a duration between an induced current event in a circuit ofthe solenoid and a valve/armature interaction event for each of theplurality of fuel injectors.
 12. The fuel system of claim 11 wherein thevalve of each of the fuel injectors includes a valve member movablebetween a first position in contact with a seat to block a pressurecontrol passage to a drain, and a second position out of contact withthe seat to open the pressure control passage to the drain; wherein thearmature of the solenoid is operatively coupled to the valve member; andthe armature is movable with respect to the valve member toward anovertravel stop when the valve member is at the first position.
 13. Thefuel system of claim 12 wherein the induced current event is associatedwith the armature contacting an overtravel stop.
 14. The fuel system ofclaim 13 wherein the end-of-current trim determination algorithm isconfigured to energize the solenoid for a plurality of diagnosticevents.
 15. The fuel system of claim 14 wherein a diagnostic on-time foreach diagnostic event is sufficiently long to move the valve member outof contact with the seat, but insufficiently long to inject fuel fromthe fuel injector.
 16. The fuel system of claim 15 wherein the solenoidis energized and de-energized twice during each of the diagnosticevents.
 17. The fuel system of claim 16 wherein each diagnostic eventincludes a first diagnostic on-time separated by a dwell from a seconddiagnostic on-time.
 18. The fuel system of claim 17 wherein the dwell ofeach diagnostic event of the plurality of diagnostic events isdifferent.
 19. The fuel system of claim 18 wherein the end-of-currenttrim determination algorithm is configured to identify which diagnosticevent of the plurality of diagnostic events has an armature bounce delaythat is smaller than the armature bounce delay of the remainingdiagnostic events of the plurality of diagnostic events.
 20. The fuelsystem of claim 19 wherein the end-of-current trim determinationalgorithm is configured to calculate an overtravel return delay for theidentified diagnostic event; and configured to determine theend-of-current trim based on the overtravel return delay.